1. Field of the Invention
This invention relates to a recording medium to be suitably used for ink-jet recording. It also relates to an ink-jet recording method using such a recording medium.
2. Related Background Art
Known ink-jet recording systems normally comprise one or more nozzles for ejecting ink droplets onto a recording medium in order to produce and record pictures and/or characters on the medium. These systems are highly versatile in terms of colors and patterns to be used for recording and adapted to high speed recording without giving off particularly annoying noise and, unlike photography, requiring development and fixing steps. Therefore, they are finding increasingly diverse applications particularly in the field of information-related devices including printers, copying machines, word processors, facsimile machines and plotters. Additionally, in view of the recent development of marketing low cost digital cameras, digital video recorders and scanners and the widespread popularity of personal computers, ink-jet recording systems are expected to be popularly used as output devices for producing images stored in them. In fact, efforts have been made for the ink-jet recording system to meet the requirements of higher recording speed and enhanced high definition and full color recording capability in order to make it competitive with silver halide type color photography and multi color printing of a plate system. In the course of the recent technological development, however, it has been recognized that the recording medium is an important subject matter on which more stress has to be put.
A number of different recording media have been proposed for ink-jet recording. For example, Japanese Patent Application Laid-Open No. 52-53012 discloses a type of ink-jet recording paper prepared by applying a coating paint on low-sized paper. Japanese Patent Application Laid-Open No. 53-49113 discloses another type of ink-jet recording paper prepared by impregnating paper incorporated with a powdery urea-formalin resin therein with a water-soluble polymeric substance. Japanese Patent Application Laid-Open No. 55-5830 discloses still another type of ink-jet recording paper prepared by forming an ink-absorbing coating layer on a surface of substrate. Japanese Patent Application Laid-Open No. 55-51583 describes the use of non-crystalline silica as pigment contained in the coating layer of ink-jet recording paper. Japanese Patent Application Laid-Open No. 55-146786 describes the use of a coating layer of a water-soluble polymeric substance.
Recently, the use of alumina hydrate has been attracting attention for recording media, because it has advantages as compared with conventional recording media. Namely, alumina hydrate shows a remarkable fixing capability for a dye in an ink and an enhanced coloring potential due to its positive electric charge so that it can produce highly glossy images. Japanese Patent Application Laid-Open No. 7-232475 discloses a recording medium in which an alumina hydrate is used for enhancing ink-absorbency and for preventing bleeding. Also, U.S. Pat. Nos. 4,879,166 and 5,104,730 and Japanese Patent Application Laid-Open Nos. 2-276670, 4-37576 and 5-32037 respectively describe recording media comprising an alumina hydrate layer with a pseudo-boehmite structure.
However, for a recording medium containing alumina hydrate to fully compete with silver halide type photography and multi color printing of a plate system in quickly producing a finely defined image, there are a lot of problems including the following that have to be solved.
(1) In case of printing a finely defined color image in a short period of time, since a large volume of ink has to be applied to the surface of the recording medium, the applied ink cannot be fully taken up into the pores of the medium and can bleed and flow over the ink-receiving surface to degrade the image on the medium.
(2) The recording medium is required to absorb ink rapidly for high speed printing, but beading may occur when the applied ink is not absorbed at a sufficiently high rate. The term "beading" as used herein refers to a phenomenon where some or all of the ink dots placed on the recording medium are mingled with adjacent ones to blur the image formed on the medium before the ink is sufficiently absorbed by the medium.
(3) Japanese Patent Application Laid-Open No. 3-281384 describes an alumina hydrate, which is in columnar form and forms an aggrgation oriented in a certain direction, and a method for forming an ink-receiving layer using such alumina hydrate. Japanese Patent Application Laid-Open No. 2-276670 describes a bundle of filaments of alumina sol. However, filament- or column-shaped particles of alumina hydrate can easily and densely agglomerate, presumably because they show a concentrated electric charge along the edges of the particles and hence it is difficult for them to permit an ink to infiltrate into the ink-receiving layer. As a result, such alumina hydrate is not adapted for ink to be used for producing high definition color images in a short period of time as beading can easily occur.